Chapter 6, Problem 6.45AP

Interpretation Introduction

(a)

Interpretation:

The complete line-and-wedge structures for the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are to be drawn.

Concept introduction:

A carbon atom that has four nonequivalent atoms or groups attached to it is known as the chiral carbon atom. Chiral carbon centers are also called as asymmetric or stereogenic centers. The compounds which have plane of symmetry along with the chiral centers are known as meso compounds. The meso compounds are achiral compounds.

Answer to Problem 6.45AP

The complete line-and-wedge structures for the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are shown below.

Explanation of Solution

The structure of $2,3,4\text{-Trichloropentane}$ is shown below.

Figure 1

The template for line-and-wedge structures of the compound with five carbon atom is shown below.

Figure 2

The meso stereoisomers of $2,3,4\text{-Trichloropentane}$ will be form when chlorine atoms attached to carbon $\text{-}2$ and carbon $\text{-4}$ have same orientation and chlorine attached to carbon $\text{-}3$ will have different orientation. Therefore, the complete line-and-wedge structures for the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are shown below.

Figure 3

Conclusion

The complete line-and-wedge structures for the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are shown in Figure 3.

Interpretation Introduction

(b)

Interpretation:

The symmetry element in meso stereoisomers of $2,3,4\text{-Trichloropentane}$ that makes the compounds achiral is to be shown.

Concept introduction:

A carbon atom that has four nonequivalent atoms or groups attached to it is known as the chiral carbon atom. Chiral carbon centers are also called as asymmetric or stereogenic centers. The compounds which have plane of symmetry along with the chiral centers are known as meso compounds. The meso compounds are achiral compounds.

Answer to Problem 6.45AP

The symmetry element in meso stereoisomers of $2,3,4\text{-Trichloropentane}$ that makes the compounds achiral is shown below.

Explanation of Solution

The structures of the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are shown below.

Figure 3

The meso compounds are divided into two equal half by a plane of symmetry. Therefore, the symmetry element in meso stereoisomers of $2,3,4\text{-Trichloropentane}$ that makes the compounds achiral is shown below.

Figure 4

Conclusion

The symmetry element in meso stereoisomers of $2,3,4\text{-Trichloropentane}$ that makes the compounds achiral is shown in Figure 4.

Interpretation Introduction

(c)

Interpretation:

The relationship between two meso compounds of $2,3,4\text{-Trichloropentane}$ is to be stated.

Concept introduction:

Those compounds which have the same molecular formula but have different arrangements of atoms are known as isomers. The phenomenon is called isomerism. The isomers are generally classified as structural isomers and stereoisomers. Stereoisomers are further divided into two categories diastereomers and enantiomers.

Answer to Problem 6.45AP

The two meso compounds of $2,3,4\text{-Trichloropentane}$ are diastereomers.

Explanation of Solution

The structures of the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are shown below.

Figure 3

The compounds are non superimosable of each other. These compounds are not mirror images of each other. Therefore, The two meso compounds of $2,3,4\text{-Trichloropentane}$ are diastereomers.

Conclusion

The two meso compounds of $2,3,4\text{-Trichloropentane}$ are diastereomers.

Interpretation Introduction

(d)

Interpretation:

Whether carbon $\text{-3}$ is a stereocenter in the meso compounds of $2,3,4\text{-Trichloropentane}$ or no is to be stated. The reason for the corresponding answer is to be stated.

Concept introduction:

A carbon atom that has four nonequivalent atoms or groups attached to it is known as the chiral carbon atom. Chiral carbon centers are also called as asymmetric or stereogenic centers. A carbon atom that does not have four nonequivalent atoms or groups attached to it is known as an achiral carbon atom.

Answer to Problem 6.45AP

The carbon $\text{-3}$ is a stereocenter in the meso compounds of $2,3,4\text{-Trichloropentane}$ because a new stereoisomer is formed when the bonds carbon $\text{-3}$ are broken and rearranged.

Explanation of Solution

The structures of the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are shown below.

Figure 3

Stereocenters define as the atom whose bond if broken and rearranged, then a new stereoisomer will form. When the bond carbon atom $\text{-3}$ is broken and rearrangement, then a new stereoisomer is formed. This process is shown below.

Figure 5

Therefore, the carbon $\text{-3}$ is a stereocenter in the meso compounds of $2,3,4\text{-Trichloropentane}$.

Conclusion

The carbon $\text{-3}$ is a stereocenter in the meso compounds of $2,3,4\text{-Trichloropentane}$ because a new stereoisomer is formed when the bonds carbon $\text{-3}$ are broken and rearranged.

Interpretation Introduction

(e)

Interpretation:

The addition to the $R,S$ system that would be required to assign a configuration to carbon $\text{-}3$ is to be stated. A new rule to assign a $R$ or $S$ designation to each carbon in the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ is to be stated. $R$ or $S$ designation to each carbon in the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ is to be stated.

Concept introduction:

The naming of the chiral center and geometric isomers are based on Cahn-Ingold-Prelog priority rules. If the priority assigned to each group attached to the chirality center in a molecule is in a clockwise direction, then it is the $R$-stereoisomer, and if this is counter-clockwise, then it is the $S$-stereoisomer. $R$ and $S$-stereoisomer are mirror images of each other.

Answer to Problem 6.45AP

The absolute configuration of carbon $\text{-3}$ is represented with $s$ or $r$ instead of $R$ or $S$ because two same groups are attached to carbon $\text{-3}$.

When all the hydrogen atoms are in same plane, then $r$ configuration is assigned to the carbon $\text{-3}$ atom. When all the hydrogen atoms are in not same plane, then $s$ configuration is assigned to the carbon $\text{-3}$ atom. The $R$ or $S$ designation to each carbon in the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are assigned as shown below.

Explanation of Solution

The structures of the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are shown below.

Figure 3

The absolute configuration of carbon $\text{-3}$ is represented with $s$ or $r$ instead of $R$ or $S$ because two same groups are attached to carbon $\text{-3}$. These same groups have different special connectivity’s.

The priorities to the groups are assigned on the basis of the atomic number.

At carbon $\text{-2}$, the chlorine atom will have the highest priority will be assigned with $1$. The methyl group will get lower priority than the carbon atom attached to the chlorine atom. The hydrogen atom will get the lowest priority and will be assigned with $4$.

At carbon $\text{-4}$, the chlorine atom will have the highest priority will be assigned with $1$. The methyl group will get lower priority than the carbon atom attached to the chlorine atom. The hydrogen atom will get the lowest priority and will be assigned with $4$.

At carbon $\text{-3}$, the chlorine atom will have the highest priority will be assigned with $1$. The two groups will have same priority. The hydrogen atom will get the lowest priority and will be assigned with $4$. The structure of compounds after assigning the priority number is shown below.

Figure 6

From the Figure 6, it can be conclude that when all the hydrogen atoms are in same plane, then $r$ configuration is assigned to the carbon $\text{-3}$ atom. When all the hydrogen atoms are in not same plane, then $s$ configuration is assigned to the carbon $\text{-3}$ atom.

Conclusion

The absolute configuration of carbon $\text{-3}$ is represented with $s$ or $r$ instead of $R$ or $S$ because two same groups are attached to carbon $\text{-3}$.

When all the hydrogen atoms are in same plane, then $r$ configuration is assigned to the carbon $\text{-3}$ atom. When all the hydrogen atoms are in not same plane, then $s$ configuration is assigned to the carbon $\text{-3}$ atom. $R$ or $S$ designation to each carbon in the two meso stereoisomers of $2,3,4\text{-Trichloropentane}$ are assigned as shown in Figure 6.

Interpretation Introduction

(f)

Interpretation:

The number of stereoisomers of $2,3,4\text{-dichloropentane}$ is to be stated.

Concept introduction:

A carbon atom that has four nonequivalent atoms or groups attached to it is known as the chiral carbon atom. Chiral carbon centers are also called as asymmetric or stereogenic centers. The compounds which have plane of symmetry along with the chiral centers are known as meso compounds. The meso compounds are achiral compounds.

Answer to Problem 6.45AP

The number of stereoisomers of $2,3,4\text{-dichloropentane}$ is $4$.

Explanation of Solution

The structure of $2,3,4\text{-Trichloropentane}$ is shown below.

Figure 1

The number of stereocenters in $2,3,4\text{-Trichloropentane}$ is $3$.

The total number of stereoisomers of a compound with a meso configuration is calculated by the formula shown below.

$\text{Number}\text{of}\text{stereoisomers}={\text{2}}^{n-\text{1}}$

Where,

• $n$ is the total number of stereocenters.

Substitute the number of stereocenters in the above expression.

$\begin{array}{rll}\text{Number}\text{of}\text{stereoisomers}& =& {\text{2}}^{3-1}\\ & =& 4\end{array}$

Therefore, the number of stereoisomers of $2,3,4\text{-dichloropentane}$ is $4$.

Conclusion

The number of stereoisomers of $2,3,4\text{-dichloropentane}$ is $4$.